The present invention relates to communication systems and more particularly to an asynchronous integrated voice and data communication system.
To date data buses or communication systems have employed either time division multiple access in which each channel that wants to use the transmission medium or bus is preassigned a time slot in which to place his message, or frequency division multiple access in which each channel is assigned a frequency slot. Such assignments can be made at the time the network is established or on a dynamic basis by a network controller to whom all users listen. A user's position in the time or frequency space of the system determines his identity.
Many forms of traffic operate on a demand cycle basis that have different structures. Telephone users are rather infrequent users (at lower levels in the hierarchy) but have extended contact times of minutes. Computers and other data sources are frequent users but have short durations of contact. Consequently, any rigid structure of bus or transmission medium time or frequency assignment will discriminate against one type of user or the other. Unfortunately, as communications grow, both types of traffic will be commonly present. The challenge is to handle both types of traffic in a transparent manner on a common channel.
Generally rigid assignment structures have been conceived and used to conserve bandwidth. However, with the utilization of fiber optic transmission technology, it can be confidently projected that in wired systems, bandwidth will significantly decrease in cost. Furthermore, with the advent of inexpensive low and medium powered computation, new transmission medium or bus operation structures become thinkable and economically attractive.
One of the central technical questions in developing an integrated data and voice transmission system has been the development of communications architectures to economically and efficiently handle data communications. The classical switching approaches to handle these communications requirements (circuit switching, message switching and packet switching) try to meet these needs while conserving transmission capacity requirements and minimizing terminal intelligence. Since these were the most expensive items in the system cost, this was really an attempt to minimize the cost per line of serving the users.
Delay and set-up times determine the applicability of these different switching approaches to different users. Voice users demand minimum delay in message delivery but can tolerate rather long set-up times. For data users the situation is reversed, since message and packet switched networks introduce delay to gain trunk use efficiency. However, commonality of voice and data service is relinquished in the process.